Treating arsenical gold ores



g- 1953 D. T. TARR, JR., Em 2,650,159 TREATING ARSENICAL GOLD ORES Filed Nov. 23, 1949 2 Sheets-Sheet 1 Feed Due to controlled deficiency of O uprising from lower 450C to less} bed, Ass fumes off;

than fusion Fe AsS As S +As O Due to controlled |e\ supply of 0 the As-free ore whose Self-roasting S has been lessened, temperature the lRON Fe O 05 650C and the residual 29 FeS "SOf" F8203 As and 8 free ore lNV S: FRANCOIS A. FISCHE 8 BD$NALD T. TA

ATTORNEY Aug. 25, 1953 Filed Nov. 23, 1949 TREATING ARSENICAL GOLD ORES 2 Sheets-Sheet 2 INVENTORSZ FRANCOIS A. FISCHER a DONALD T. TARR,JR.

F|G.2. M

ATTORN EY Patented Aug. 25, 1953 TREATING ARSENIOAL GOLD ORES Donald T. ,Tarr,Jr., Denver, 0010., and Francois A. Fischer, Brussels, Bel

slum, assign rs to The Don Company, Stamford C ofDelaware nit, a rporatio Application November 23, 1949, Serial No. 128,962

2 Claims.

This invention relates to the roasting ofarsenopyrite ores and particularly to the roasting of those gold bearing arsenopyrite ores which contain commercially significant amount of gold in association with the mineral arsenopyrite.

A gold bearing ore consisting essentially of arsenop rite, pyrite, stibnite, with lesser amounts of other sulfide materials, together with such gangue or rock minerals as carbonates of lime, magnesia, etc., with quartz was used for the experimentationleading to the invention disclosed herein. This type of arseno-pyrite gold bearing ore contains its cold values in several forms. There is present so-called free gold which may be recovered by any of the usual methods of chemical or mechanical concentration. In addition to this free gold there is a commercially valuable quantity of gold which is not responsive to ordinary means of recovery. Attempts have been made to recover this gold by roastin metllflds f l y ovanidin the roasted ore. But, heretofore, in attempting to recover these normally unavailable gold values; rocesses h ve been developed which might be characterized by the teat that, in general, they requ re rg omplex equipment involving a high initial installacause the ore at those points becomes no longer self-roasting. Because of these factors, many gold ores which contain small quantities of gold, or many gold ore tailingsno longerbecome economically feasible to work and must be rejected. This is particularly true of low-sulfide ores which are not self-sustaining and which require the expensive application of extraneous fuel.

In order to'recover these unrecoverable gold values it is necessary to release them from their original combination in the ore and thus make them amenable to cyaniding. To so release them the ore must be roasted so that every particle is fractured. It must be a complete roast, i. e., one containing no residual unconverted mineral still presentin its original, natural state of chemical combination.

If theore is not completely roasted, then ferruns iron will be present in the final product and iron will be a largeconsumer of cyanide, otherwise knownas a cyanicide. If the amount of cyanicideis high, then the cyanide consump tion is increased and the economic worth =ofthe process is serious iieopandized. Thusthe one must becompletely roasted, resulting inthe conversion of theierrous iron to the ferric state, in which stateit is not detrimental. v r 1 However, when the or completely ro s ed, thearsenic is converted to its highest oxidation state, namely, $205, in which form itiis not volatile. Thus it remains behind in the ore nd serve to plug the pores, preventing cyanide solutionirom reaching theentrapped gold v lu s.

Thus the problem resolves itself to one in which there mu t be a compl tely r aste ore a d yet which must not contain A5205, which in itself is the necessary product of a complete oxidation or roast.

The roasting of arsenopyrite eoldores in conventional equipment usin conventional means s known and in these pocesses, oxidation of elements originally present in mineral arseno yrite and associated oxidizable minerals m y be c rried substantially to completio,

By using conventional equipment, th c l r of the roasted produ t i .known to vary from ac to red, but operators report that the red ro st is the highly desirable one be aus fe rous iron is absent.

In these processes, because of the poor control over both oxygen input and roasting temper-aadded to obtain a .completely roasted product fromthese lowsulfide ores. l

These objects are attainable by roasting the ore under fluidizing conditions in two stages with Before presentingn detailed description of apparatus and r-process constituting the invention suspending gas velocity is quite low;

hereof, it is important to note that according to this invention the roasting of ore is accomplished in a fluidizing furnace or reactor in which the ore is in a fluidized condition.

A fluidized solids reactor or roaster or furnace in its mostsimple form is a vertical vessel having a perforated horizontal partition in its lower portion. Finely divided solids are supplied to the vessel above the partition by gas is passed upwardly from the bottom of the vessel through the partition andithrough the powdered solids. The gas passes through the solids at such a rate that the solids are kept as a suspended bed or layer in the vessel. The solids are in dense, turbulent suspension and are usually referred to as a fluidized bed.

A fluidized bed is a very dense suspension of a conduit and fine solids in a supporting flowing gas. The

density or solids-concentration per unit volume of such a fluidized bed is very high, being commonly of the order of 10 to 100 pounds of solids per cubic footof bed volume, This bed density is to be contrasted with typical dilute dispersions or suspensions, such as dusty air wherein the density of solids concentration is of the order of only of a pound per cubic foot of the dispersion. In addition, the solid particles of a fluidized bed are in a high'state of turbulence or erratic, zig-zag motion in the bed even when the this high turbulence causes intimate and rapid mixing of the solids particles so that in a typical bed complete mixing of the solids appears to take place instantaneously. A fluidized bed, because of its high density and great turbulence, is noted for the rapid transfer of heat between its solid and gaseous components; this heat transfer is so rapid that a remarkable uniformity or homogeneity in the temperature of the bed results.

detail, a fluidized solids reactor con- 9, gas-tight chamber closed at a plate perforated to permit In some the bottom with upflow and secure uniform flow-distribution of gases admitted to a windbox below the plate; means for admission of sub-divided material to be roasted, and means for removal 'of roasted material as well as means forremoval from the reactor of the gas after it is reacted with fluidized particles therein. The gas passes into the windbox, thence upwardly through the per- .foratedplate, (hereafter referred to as the constriction plate) and through a mass of the finely divided solids to be roasted. The velocity of the gas through the mass or layer or bedof finely divided solids (hereafter referred to as the fluid- .ized bed) is controlled so that it suflices to produce an exceedinglyturbulent agitation of the solids through which the gas is passing and which by its passage are densely suspended and, in general, caused to behave like a boiling liquid including being capable of presenting a fluidlevel. This velocity, as measured in the upper portion of the reactor above the level of the densely suspended solids, is commonly of the order of 0.2 to 2.0 feet per second,.and is referred to as superficial velocity. The velocity of the gas, while it is essential that it be in a range suf-, flcient to fluidize the fuel solids, must be below the rate at which all or substantially all of the solids suspended would be entrained and carried quickly out of the reactor as a dispersed or dilute suspension in the exit gas. .Such a dispersed suspension behaves substantially like the exit gas and is unlike the fluidized .bed. The meansfor removal of. roasted solids from thelreactor'will 1 process.

tion of conditions roasted ores. The conditions in the reactor may usually comprise a vertical or steeply inclined conduit leading outside the reactor and provided with means for permitting a free discharge of the solids but not a free discharge of gases from the chamber. The minimum depth of the fluidized bed of solids within the reactor may be determined by the elevation of the discharge means as measured upward from the constriction plate.

The depth will commonly be of the order of l to 5 feet.

The approximate fluidizing velocity, the best depth of the fluidized bed, temperature control methods and other conditions of operation hereinafter referred to, which give the best results, may be determined by preliminary test on the particular ore which is to be roasted by our According to this invention, therefore, the roasting of the arseno-pyrite ore is carried out in an apparatus which permits accurate regulaaifecting the quality of the be readily determined at any time and adjusted as required or the operations of the roasting apparatus may be automatically regulatedwithin desired limits, as we shall subsequently disclose. In roasting an arsenopyritic gold bearing ore by our process, flnelydivided particles of the ore are introduced to the upper bed in the primary zone of the reactor above the apertured constriction plate and a free oxygen-bearing gas is upflowed through the constriction plate at a rate sufficient to maintain the ore particles in'a violent, turbulent, mobilized condition of dense fluidized suspension. The bed of mobilized or fluidized ore will act like a liquid in that it is capable of presenting a level, will flow like a liquid under hydraulic head and, most pertinently, will have substantially homogeneous tem perture conditions throughout the bed depth. The oxygen bearing gas must satisfy the dual re-, quirement of being supplied at to maintain the particles in a fluidized state and containing a sufficient quantity of oxygen to controlledly oxidize the ore to the proper degree which this invention teaches. i This partially oxidized ore then flows to the lowerv bed in the secondary zone where in the carefully controlled oxygen-bearing gas again fluidizes it and completes the roasting or oxidation of the sulfldie constituents. The product is removed from this second bed by a downwardly slanting pipe, the height of the upper end of which controls the level of the bed. This product has been discovered to be substantially com-,- pletely' roasted, is the desirable red color, and will give a high gold recovery with low cyanide consumption.

The novel features of this invention willbe understood and more fully appreciated fromthe following description, particularly when considforming the two bedembodiment of invention and wherein and by whichthe invention may be commercially realized.

More particularly, Figure 1, shows the ore feed entering bed l1, passing down the downcomer [9 into bed 18-. After roasting, the. Ore. product is removed through conduit.29..

a rate suiflcient Figure l is a simplified flow The, legends,

show chiefly the reactions, temperatures and ly niay now beshut down. Gradually the level products in theprocess. of fluidized solid in bed I I builds up until the In Figure 2, there is shown a vertical cylininlet level of downcomer I9 is reached, wherebottom member I 4 and .side walls I2. Internally, the upper end of takeoff conduit 29. These solids the vessel II is lined with refractory brick I5. accumulate in fluidized state until their level has two horizontal apertured partitions 3| and reaches the upper end of conduit :29 whereupon 33 therein which are each adapted to support they flow, controlled by valve 38, to a point outfluidized beds I1 and I8 respectively, and has 10 side reactor II where they are cyanided or otherhorizontal gas impermeable partition BI to sepawise treated for recovery of their gold values by bed II; the secondary treatment zone S is the portion of reactor .Il Occupied by bed I8. Downterm theoretical oxygen as used therein, By comer I9 leads from the surface level of bed I1 theoretical oxygen is meant that quantity of oxyto a point below the surface level of bed I8 and gen which will be stoichiometrically capable of serves to conduct treated solids in bed I1 to bed converting Fe into F6203, S into S02, As lid-AS203 I8. In this particular embodiment, the upper andMinto M02. I I

end of downcomer I9 also serve to determine the We have determined and demonstrated that level or height of bed ITI. Above bed I1 is freethe practical and commercial mode of practicing board zone 21 and above bed I8 is freeboard zone our invention is substantially as follows. The 20. Fine solid particles of metallurgical sulfides starting ores which were used are demonstrated are supplied to top bed H by means of a screwbelow. I

conveyor 42 in casing 45, which in turn is sup 25 plied by hopper 43. The conveyor 42 is driven Sampler, Fe s As Sb Au by motor 44. Gas for fluidizing and treating the I solids in beds I1 and I8 is supplied to the lower Page? Perceni Pefient Per e OzJton portion of vessel II by means of conduit 40am! 22 75 18 6 4 95 therate thereof controlled by valve 4i. The 13.' 141 horizontal P t o 33 and enter bed After arsenic and gold values vary over a wide range iiuidi ing bed 1 0 gas rises freeboard and that the sulfur value is, in general, fairly zone 20 and pa se th gh conduit 50 into F low. In terms of old processes, the sulfur value clone 51 wherein the fines which w carried of sample #3 may be said to be in the range in 1 in the gas stream are separa These which the ores would not be self-roasting withlines frequently represent completely roasted finout extraneous fue1 shed roduct and a 1 WQuIdI b drawn Ofi After the process has undergone the starting thro gh conduit 52, Controlled by valve 53- The up procedure, as previously outlined, the oxygen ond 54 n o md box Pa e u d arbitrarily, it contains only or theoretical through aperturesfi of horizontal part l n oxygen. Necessarily included in the gas will be o ed l' From d 17, th gas flows up through, the volatile products from the secondary zone, freeboard zone 21, leaves rea r I y means of 45 the principal constituent of which is sulfur dibecome completely roastedarsenic from the ore. This figure is selected only In St rt D e process as-depicted in for convenient operation and it has been found ure 2, air nder controlled pressure is suppli that any amount short of 100% of theoretical vessel ll h gh nd T s is added oxygen may be supplied, just so long as substanfuel such as natural gas which is ignited Wit 55 tially no free oxygen is found in the exitinggas,

and also to cover the lower end of downcomer in th react s. Usin 50% of theoretical oxyl9 to prevent short circuiting of infiuent air. It gen, and at a bed temperature of 505 (3., it was has been found that the height and length of discovered that 60% of the arsenic was elimithe downcomer I 9 must be so determined that nated, Maintaining the same oxygen input, but the weight of the solids therein will be sufiicient raising t temperature of th bed in th primary to overcome the as pressure in the secondary zone to 550 0., proved that 94% 0f the arsenic zone, so as to prevent this short-circuiting of the wa li inat d,

gas p the downcomerd l1 ay be pplied Thi substantially arsenic free ore now flowed with the above mentioned inert material by down to the secondary zone. The sulfur content screw-conveyor 42; bed I8 may be so supplied at this point was about 50% of the original sulfur by blowing the material back up outlet pipe 29. 7 content of the ore. Air was passed through this When the vessel II is up to a sulfide oxidizing secondary zone at such a rate that it contained temperature of about 800 0., fine metallurgical of the theoretical requirement. The temsolid sulfide particles are supplied to bed I1 by perature was found to be optimum at 625 C. screw-conveyor 42. These ores become self- However, since a fully roasted product is desired roasting exothermally and the auxiliary fuel sup- 7 here, the temperature may be permitted to vary so as to accomplish this. The limiting range of temperature is the fusion point of the material in the condition in which it comes from the primary zone. Slight amounts of impurities, such as lead, will cause this temperature to vary. The material must not be permitted to fuse, however, as this condition is anathema to fluidizing media and a dead bed will result. From a practical operating point of view, if the temperature of the secondary or lower bed is noticed decreasing it means that the oxygen in the upper bed is nearing 100% of theoretical and consuming nearly all of the sulfur in the uper bed, thus permitting very little of it to come through some lower bed to be consumed. Under these circumstances, if the ore feed rate is'increased, with oxygen remaining constant, it will result in the ore leaving the primary zone having a higher sulfur content. The roasting temperature of the lower zone will then be seen to increase. Thus a very fine control over the reaction may be obtained at all time and the low-sulfur ores may always be maintained as self-roasting in both zones.

If the temperature tends to run away at any time, water sprays 72 are provided to control it andprevent fusion of the material.

When arsenopyritic gold bearing ore is subjected to the process described in this invention, it-will always be recovered from the reactor as a red calcine, indicating a complete roast. When this red calcine is subjected to cyanidation to remove the gold, approximately 93% of the gold is extracted. The amount of cyanide necessary to obtain this high gold recovery is approximately 23 lbs. per ton of ore, and the process becomes economically feasible. With the apparatus herein described, this process is capable of close control as regards temperature, feed and infiuent oxygen yielding in' a self-sustaining roasting operation a product from which the gold recovery becomes economically feasible.

It is also within the ambit of this invention to supply fuel to the fluidized bed for those ores whose sulfur value is so low that even with this process they are not self-roasting. By so supplying fuel to the bed, it will be caused to burn directly in the bed itself and thus its maximum heat value will be utilized. Coupling this with the efficient complete use of the heat furnished from any sulfur available, gives a process which can readily be seen to be usable for the'poorest of ores.

We claim:

1. The continuous process for roasting finelydivided gold-bearing arsenopyrite solids to render their gold values amenable to cyanidation with minimum cyanide consumption, comprising the steps of establishing and maintaining a fluidized treatment bed of such solids in a primary treatment zone by feeding solids thereto and passing therethrough at solids fluidizing velocities an uprising stream of freeoxygen bearing gas while maintaining the solids at roasting temperatures less than fusion temperatures, and under such conditions effecting substantial removal of arsenicias' volatile arsenic compounds to yield partially roastedarsenic-free solids by regulating the quantity of free-oxygen in the uprising gas stream to be an amount sufficient to oxidize a portion of the sulfide-sulfur content of the solids to sulfur-dioxide but insufficient to so oxidize all of such sulfur, discharging gases including volatile arsenic compounds from the bed and from the zone, discharging partially roasted arsenic-free solids from the primary zone to a secondary zone to establish in the latter zone a bed of such solids, treating solids of the latter bed under solids fluidizing conditions to yield substantially completely roasted solids by maintaining the bed at roasting temperatures less than fusion temperatures while passing therethrough at solids fiuidizing velocities an uprising stream of gas initially containing free-oxygen in an amount at least sufficient to substantially oxidize all residual unoxidized oxidizable constituents of the bed solids, discharging gases from the zone, and discharging substantially oxidized arsenicfree solids from the zone.

2. The process according to claim 1 wherein the quantity of free-oxygen supplied to the secondary treatment zone is sufficient so that gases discharged from that zone contain residual freeoxygen in an amount suflicient to oxidize to sulfur-dioxide at least a portion of the sulfide-sulfur content of the bed solids in the primary treatment zone but insuflicient to oxidize all of such sulfur to sulfur-dioxide, and the free-oxygen bearing gases supplied to the primary zone comprise the gases discharged from the second zone.

DONALD T. TARR, J R.

FRANCOIS A. FISCHER. References Cited in the file of this patent I UNITED STATES PATENTS Number Name .Date

1,941,592 Bacon et al. Jan. 2, 1934 2,444,990 Hemminger July 13, 1948 OTHER REFERENCES Canadian Mining andMetallurgical Bulletin, April, 1949, pages 178-187.

Chemical Engineering, Deo.', 1947, page 114. 

1. THE CONTINUOUS PROCESS FOR ROASTING FINELYDIVIDED GOLD-BEARING ARSENOPYRITE SOLIDS TO RENDER THEIR GOLD VALUES AMENABLE TO CYANIDATION WITH MINIMUM CYANIDE CONSUMPTION, COMPRISING THE STEPS OF ESTABLISHING AND MAINTAINING A FLUIDIZED TREATMENT BED OF SUCH SOLIDS IN A PRIMARY TREATMENT ZONE BY FEEDING SOLIDS THERETO AND PASSING THERETHROUGH AT SOLIDS FLUIDIZING VELOCITIES AN UPRISING STREAM OF FREE-OXYGEN BEARING GAS WHILE MAINTAINING THE SOLIDS AT ROASTING TEMPERATURES LESS THAN FUSION TEMPERATURES, AND UNDER SUCH CONDITIONS EFFECTING SUBSTANTIAL REMOVAL OF ARSENIC AS VOLATILE ARSENIC COMPOUNDS TO YIELD PARTIALLY ROASTED ARSENIC-FREE SOLIFS BY REGULATING THE QUANTITY OF FREE-OXYGEN IN THE UPRISING GAS STREAM TO BE AN AMOUNT SUFFICIENT TO OXIDIZE A PORTION OF THE SULFIDE-SULFUR CONTENT OF THE SOLIDS TO SULFUR-DIOXIDE BUT INSUFFICIENT TO SO OXIDIZE ALL OF SUCH SULFUR, DISCHARGING GASES INCLUDING VOLATILE ARSENIC COMPOUNDS FROM THE BED AND FROM THE ZONE, DISCHARGING PARTIALLY ROASTED ARSENIC-FREE SOLIDS FROM THE PRIMARY ZONE TO A SECONDARY ZONE TO ESTABLISH IN THE LATTER ZONE A BED OF SUCH SOLIDS, TREATING SOLIDS OF THE LATTER BED UNDER SOLIDS FLUIDIZING CONDITIONS TO YIELD SUBSTANTIALLY COMPLETELY ROASTED SOLIDS BY MAINTAINING THE BED AT ROASTING TEMPERATURES LESS THAN FUSION TEMPERATURES WHILE PASSING THERETHROUGH AT SOLIDS FLUIDIZING VELOCITIES AN UPRISING STREAM OF GAS INITIALLY CONTAINING FREE-OXYGEN IN AN AMOUNT AT LEAST SUFFICIENT TO SUBSTANTIALLY OXIDIZE ALL RESIDUAL UNOXIDIZABLE CONSTITUENTS OF THE BED SOLIDS, DISCHARGING GASES FROM THE ZONE, AND DISCHARGING SUBSTANTIALLY OXIDIZED ARSENICFREE SOLIDS FROM THE ZONE. 